Lorenzo led the title race earlier this year but has since fallen dramatically off the pace with Spanish compatriot Marc Marquez having already wrapped up the championship.
Rubbing further salt into the wounds was seeing Rossi seal second spot in the standings leaving Lorenzo with just third place to target before he heads to Ducati in 2017.
"The season is almost over and finally we arrive to Valencia, where I have some good memories, especially last year when we were able to achieve our goal and become world champion again," said Lorenzo who also won at the track in 2010 and 2013 in the elite category.
During his time at Yamaha, Lorenzo has won 43 races, gained 106 podiums, and started from pole 38 times.
"Valencia is going to be a very special race for me because after nine years with the Yamaha family I have to say goodbye and it won‘t be easy," added Lorenzo who is being chased by British Grand Prix winner Maverick Vinales on a Suzuki for third spot in the championship.
"I had a lot of good feelings with Yamaha and together we won a lot of races and titles. So I will do my best to try to win and I will try to secure third position in the championship as well."
Lorenzo has won three of the 17 races so far – the Qatar season-opener followed by back-to-back victories at Le Mans and Mugello in May.
Those performances placed him at the top of the championship before Marquez on the dominant Honda ran away with the series.
It was a third world title for the 23-year-old Marquez and was wrapped up in Japan with three races to spare.
